This invention relates to a small-size electronic sphygmomanometer.
The electronic sphygmomanometer includes an analog circuit and logic circuit.
In the analog circuit, which includes transistors, all the transistors operate in the active condition and dissipate high power.
Particularly, a semiconductive pressure transducer is required to operate by flowing relatively large current because the sensitivity of the transducer is proportional to the current value applied to it.
An operational amplifier is used in a pressure detection section and the elements used in the operational amplifier must be selected in view of offset voltage and temperature drift.
Further, external noise has to be considered in the case of amplification of alternating current.
On the other hand, it is advantageous that the logic circuit be operated in a saturation condition.
Accordingly, the logic circuit is capable of being formed as a C-MOS circuit fabricated on one chip.
Referring again to the analog circuit, the analog circuit includes a large number of resistors and capacitors in addition to bipolar transistors.
It is difficult for a small-size sphygmomanometer to be driven with low voltage and current because the desired amplitude of the signal voltage cannot be obtained using low voltage and current.